The plug-type heating elements of the prior art consist of a series of metal rectangular sections which have an insulator on each side of each section at a plurality of spaced locations along the length of the section. The electrical heating wire is wound around each of the spacers, down one side of the frame and back up the opposite side of the frame.
One problem with the prior art heating element construction involves the space taken up by each frame member. The space interferes with the flow of air through the plug unit. In other words, the heating elements, when electrically connected, provide a source of heat with the flow of air passing through and around the heating elements determining the quantity of heat emitted from the plug unit. If air flow is restricted by metal frame sections, the kilowatt output per unit area will be decreased causing loss of efficiency. Likewise, the use of multiple frame sections for a plug unit results in a large percentage of the physical space being occupied which otherwise could be used for heating elements.
Another problem of the prior art is that the insulators, attached to the frame sections, are difficult to remove and each insulator must be removed from the frame section separately in order to change wire spacing or otherwise repair the plug units. Additionally, the cost of construction, necessitated by the multiple frame sections and the attachment of each individual insulator to the frame sections, increases with the cost of materials for the frames and insulators, as well as the labor involved in assembling a plug unit.
This invention is an improvement in the electric heating element disclosed in my earlier U.S. patent application Ser. No. 20,594, filed Mar. 14, 1979, now U.S. Pat. No. 4,243,872, issued Jan. 6, 1981.